If you are on a Mac the easiest way to get it is click on the Apple menu button and choose Software Update. For Windows users you can get it from the iTunes download page.
So what’s in the update? First, there is support for syncing with IOS 4.3 devices. The update will only be available on March 11. That is the same date that the iPad 2 will be available. However, you should download iTunes 10.2 before you unwrap your iPad 2 so you can get going immediately when it arrives.
The other thing Apple listed is an improvement to Home Sharing. As a result of this update devices with iOS 4.3 will be able to browse and play content in the iTunes library through a local network.
For more information about the update check out Apple’s support article.